It is common to manufacture parts from many types from sheet materials. Specifically, the manufacture of sheet metal parts is well known.
One approach to producing sheet metal parts that is known in the prior art is to fabricate metal parts from sheet metal blanks cut from a generally planar piece of metal stock. Blanks are typically cut using punch and die sets which punch the blank from the metal sheet in a single operation. Once the blank is produced it may be further formed through other operations such as drilling, or die or roll forming. The drawback associated with this approach is that the tooling necessary to produce the blank as well as to perform the subsequent operations is specifically made to produce a specific part. This may require a significant outlay for special tooling which adds to the cost of producing the parts.
A more recent alternative to the approach of producing parts from sheet materials using dedicated tooling is the use of programmable high speed multi-punch machines. Such machines use relatively small standardized punch and die shapes to punch a series of holes in a piece of sheet material. The machine punches adjacent holes at high speed so as to define the contours of one or more parts. Such machines enable the punching of parts from a single sheet, in a cookie-cutter fashion, using standardized and inexpensive tooling. An example of programmable high speed multi-punch machines are machines produced by Trumpf, Inc. of Farmington, Conn.
During production of parts on programmable multi-punch machines it is necessary to maintain the metal part being fabricated in place relative to the sheet until all the contours of the part have been defined by the punching of openings. This is accomplished by leaving small fingers of material called "tabs" or "webs" that extend across the openings which separate the area of the sheet that will become the part from the external portion of the sheet that will not become part of a part. The tabs hold the part portion solidly connected to the sheet during punching operations by various tools. This enables the sheet to be moved rapidly and precisely by an automated positioning mechanism to enable the precise punching of openings at the desired locations under the programmable control of the machine.
The tabs are sufficiently wide and strong so as to hold the parts portions in place, but are thin enough to enable the parts to be readily separated from the rest of the sheet. The separation of the parts is accomplished after the punching operations are completed, usually by shaking the sheet. This deforms the sheet. Because the parts portions are connected to the sheet only by the thin tabs, the deformation of the sheet creates stresses in the tabs that causes them to break. As a result, the parts portions fall out of the sheet or other work piece, and are ready for other processing. The external portions of the piece which do not become parts are recycled, as are all of the slugs that are cut out of the sheet during the punching process.
The significant advantage of such high speed fabrication is that punches of various types may be used to define the contours of the particular part. Such punches may include geometric figures as well as punches having curved faces which enable the production of rounded pieces. Such tooling may also be used to produce internal part features such as holes or slots. This avoids the need for subsequent operations to produce these features. As a result, parts may be manufactured more quickly, at higher quality and at a lower cost.
A significant drawback associated with producing parts using high speed programmable multi-punch machines is that the parts often have burrs produced by metal from the tab that remains with the part after it is removed from the work piece. These burrs are generally sharp. If the parts produced are going to be located in an area where they will come in contact with a person's fingers or skin, the burrs must be removed to prevent cuts and scrapes. It is also common for parts to be in sliding engagement with other parts. Burrs that result from residual tab material may hinder the parts ability to perform its intended function. As a result, it is often necessary to remove such burrs.
Unfortunately, the removal of such burrs from parts produced on programmable multi-punch machines is somewhat difficult. This is because the burrs reside along the relatively thin side wall of the part. It is difficult to remove such burrs using automatic equipment because it is difficult to handle the parts in this orientation. Often it is necessary for an individual to manually flatten or remove the burrs using a file, grinding wheel, or belt sander. Such operations are time consuming and expensive. Further, because such operations are not automated and are generally performed by individuals not having a high degree of skill, the quality of the burr removal operation is often not as great as is desired.
An alternate method for similar fabrication of parts on a programmable multi-punch machine is to punch the complete contour without the use of the holding tabs. With this method, the part is separated from the external portion of the sheet when the last material is punched. Based on the size of the part, the machine is then programmed to either stop or to eject the part down a chute into a receiving bin. When the machine stops (for large parts), the operator has to manually remove the completed part and restart the machine. When the parts are ejected down a chute (for small parts), the machine continues to run, but the punching cycle is delayed while the chute opens and closes. Both of the alternatives create undesirable production delays. The chute method adds another potential problem of part distortion depending on how the parts fall and land on one another in the receiving bin. Therefore, neither method is acceptable for long term quality production.
Thus, there exists a need for a device and method that may be used to produce generally burr-free parts on a programmable punch machine.